The present invention is directed to a light directing arrangement and method for use with a display apparatus, and more particularly to a light directing arrangement that directs an image to an angle different from a glare angle and is resistant to corrosion.
Liquid crystal displays (LCDs) are used in many different types of electronic devices, including portable computers, cellular phones, and digital watches. One class of LCD, which is substantially reflective, often includes a reflector for directing ambient light to the viewer. Another class of LCD often includes a partially transmissive reflector for also allowing light from a light source within the device to convey information to the viewer. A partially transmissive reflector is commonly called a transflector, and an LCD that incorporates a transflector is commonly called transflective. The reflector may be made of metal or other types of composite materials. Some examples of LCD devices are discussed in co-pending application, xe2x80x9cOptical Devices Using Reflecting Polarizing Materialsxe2x80x9d, U.S. Ser. No. 09/298,003, filed Apr. 22, 1999.
The present invention is a light directing construction that utilizes a structure that protects against corrosion initiated by salt environments. The present invention is not directed to the increase of adhesion between the various layers of the light directing construction. More particularly, the corrosion resistant features disclosed herein are directed at removing at least one of the three components that together lead to a particular type of corrosion in this construction: salt, water, and an oxidizer. Removal of at least one of these components from the intimate environment of the light directing construction minimizes, and preferably eliminates, corrosion.
The light directing construction includes a light directing film and a thin transflective layer of metal disposed on the light directing film. The light directing film includes a three-dimensional prismatic structure made from UV-curable organic materials; the prismatic structure has two sides, where one side includes saw-tooth formations with tilted surfaces. The transflective metal coating is disposed on the side of the prismatic structure with the saw-tooth formations.
The light directing construction further includes a corrosion resistant feature that minimizes any corrosion that may occur between the metal coating and the prismatic structure when the light directing construction is exposed to an environment having salt present. In one embodiment of the present invention, an intermediate layer is positioned between the light directing film and the metal coating. This intermediate layer can be a thin metal coating between the light directing prismatic structure and the thin metal coating. The intermediate layer metal can be selected from one or more of chromium, nickel, iron, aluminum, titanium, silver, gold, zirconium, platinum, alloys containing these metals, and other metals. Preferred intermediate layer metals are alloys of nickel-chromium and nickel-chromium-iron at a thickness of about 2 to 40 angstroms.
In another embodiment, a polymeric peripheral coating is provided on the outer circumference of the light directing construction, thereby sealing the open edges of the construction and the points of entry of any corrosion initiating reagents. In a preferred aspect, the polymeric peripheral coating is provided by using a laser beam. The laser beam melts at least partially the outermost edges of the light directing construction, thereby creating flowable material that seals the outer edges of the construction. The laser beam can be used simultaneously to cut the light directing construction to a desired shape and size and provide the edge sealing.
The prismatic structure that provides the base for the display apparatus is formed of UV-curable cross-linked resin, such as an epoxy-acrylate. The three-dimensional, tilted surfaces of the prismatic layer may have a tilt angle of about 1xc2x0 to 35xc2x0 from horizontal. The saw-tooth formations may have a repeat distance of at least about 5 micrometers, and no greater than about 200 micrometers.
The transflective metal coating, which is disposed on the structured surface of the prismatic structure, can be silver, chromium, nickel, aluminum, titanium, aluminum-titanium alloy, gold, zirconium, platinum, palladium, aluminum-chromium alloy, rhodium, or combinations. The transflective metal coating is preferably silver, is typically no thicker than 400 Angstroms, and has at least 10% or greater transmission of visible light.
The light directing construction, which includes the light directing film, the transflective metal coating, and the corrosion resistant feature, further can include an inorganic protective layer formed on the transflective metal coating, wherein the inorganic protective layer inhibits molecular transfer to the metal coating from the atmosphere and balances the color of reflected and transmitted light. The inorganic protective layer can include titanium, indium tin oxide, zinc sulfide, tin oxide, indium oxide, titanium oxide, silicon dioxide, silicon monoxide, or magnesium fluoride.
Further, the light directing construction can include a polymer barrier layer or polymer protective layer to inhibit molecular transfer to the transflective metal coating. This layer can be selected from the group consisting of cross-linked epoxy resin, cross-linked or linear acrylic resin, epoxy acrylate, polyester, polyethylene, polyvinylidene chloride, and polyvinyl alcohol.
A pressure sensitive adhesive layer further can be provided between a polarizer and the inorganic protective layer. The pressure sensitive adhesive layer overlying the inorganic protective layer may be an acrylate/acrylic acid adhesive layer, the adhesive layer being optically diffuse. The pressure sensitive adhesive layer may include optical diffuser particles.
The light directing film of the present invention, with any of the optional coatings and features, can be incorporated into a display apparatus.
In one specific embodiment, the present invention is directed to a light directing construction, comprising a prismatic structure having first and second surfaces, the second surface including saw-tooth formations having tilted surfaces; the prismatic structure made from a non-halogenated UV polymerizable composition; a transflective metal coating is provided proximate to the saw-tooth formations; the transfiective metal coating having a transmission of at least 10% of visible light; and a corrosion resistant feature disposed proximate to each of the metal coating and the prismatic structure, the corrosion resistant feature providing a decrease in the sum of transmission and reflection of visible light of less than 5%. In some embodiments, the decrease in the sum of the transmission and reflection is less than 2%.
In one embodiment, the corrosion resistant feature is an intermediate layer disposed between the prismatic structure and the transflective coating. In another embodiment, the corrosion resistant feature is a polymeric coating disposed-on the periphery of the construction. This polymeric coating can be formed when the construction is cut with a laser.